When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Conjugated polymer-based chemical sensors.

Using a simple hydrothermal procedure, cobalt oxide (Co3O4) nanowires were in situ synthesized on three-dimensional (3D) graphene foam grown by chemical vapor deposition. The structure and morphology of the resulting 3D graphene/Co3O4 composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectroscopy. The 3D graphene/Co3O4 composite was used as the monolithic free-standing electrode for supercapacitor application and for enzymeless electrochemical detection of glucose. We demonstrate that it is capable of delivering high specific capacitance of ∼1100 F g–1 at a current density of 10 A g–1 with excellent cycling stability, and it can detect glucose with a ultrahigh sensitivity of 3.39 mA mM–1 cm–2 and a remarkable lower detection limit of <25 nM (S/N = 8.5).

3D Graphene–Cobalt Oxide Electrode for High-Performance Supercapacitor and Enzymeless Glucose Detection

Over 7,000 peer reviewed articles have been published on electrochemical glucose assays and sensors over recent years. Their number makes a full review of the literature, or even of the most recent advances, impossible. Nevertheless, this chapter should acquaint the reader with the fundamentals of the electrochemistry of glucose and provide a perspective of the evolution of the electrochemical glucose assays and monitors helping diabetic people, who constitute about 5 % of the world’s population. Because of the large number of diabetic people, no assay is performed more frequently than that of glucose. Most of these assays are electrochemical. The reader interested also in nonelectrochemical assays used in, or proposed for, the management of diabetes is referred to a 2007 excellent review of Kondepati and Heise [1].

Electrochemical glucose sensors and their applications in diabetes management.

Platinum nanoparticles with a diameter of 2-3 nm were prepared and used in combination with single-wall carbon nanotubes (SWCNTs) for fabricating electrochemical sensors with remarkably improved sensitivity toward hydrogen peroxide. Nafion, a perfluorosulfonated polymer, was used to solubilize SWCNTs and also displayed strong interactions with Pt nanoparticles to form a network that connected Pt nanoparticles to the electrode surface. TEM and AFM micrographs illustrated the deposition of Pt nanoparticles on carbon nanotubes whereas cyclic voltammetry confirmed an electrical contact through SWCNTs between Pt nanoparticles and the glassy carbon (GC) or carbon fiber backing. With glucose oxidase (GOx) as an enzyme model, we constructed a GC or carbon fiber microelectrode-based biosensor that responds even more sensitively to glucose than the GC/GOx electrode modified by Pt nanoparticles or CNTs alone. The response time and detection limit (S/N = 3) of this biosensor was determined to be 3 s and 0.5 microM, respectively.

Electrochemical biosensing platforms using platinum nanoparticles and carbon nanotubes.

Ultralayered Co3O4 structures with high porosity have been synthesized by a facile homogeneous precipitation process under hydrothermal conditions. The superstructures consist of well-arranged micrometer length rectangular 2D flakes with high specific surface area, pore volume, and uniform pore size distribution. The electrochemical measurements demonstrate that charge storage occurs in ultralayered Co3O4 due to reversible redox reactions. The charge–discharge study shows that the material is capable of delivering very high specific capacitance of 548 F g–1 at a current density of 8 A g–1 and retains 66% of capacitance at 32 A g–1. The charge–discharge stability measurements show excellent specific capacitance retention capability, ca. 98.5% after 2000 continuous charge–discharge cycles at high current density of 16 A g–1. The exceptional cyclic, structural, and electrochemical stability at higher current rate with ∼100% Coulombic efficiency, and very low ESR value from impedance measurements promise good...

Ultralayered Co3O4 for High-Performance Supercapacitor Applications

Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions

Voltammetric and XPS investigations of nickel hydroxide electrochemically dispersed on gold surface electrodes

The electrocatalytic oxidation of aliphatic alcohols in alkaline solutions at a nickel-based chemically modified glassy carbon electrode (Ni-CME) was investigated. The electrode was characterized by voltammetry and flow injection and applied for amperometric detection of mono- and polyhydric alcohols separated by liquid chromatography. A mechanistic electrooxidation model is proposed that involves a Langmuir-type adsorption process on different sites: NiO and NiOOH for polyhydric and monohydridic compounds, respectively. The process is followed by a hydrogen abstraction from the carbon α to the OH group through a radical pathway in the rate-determining step

Innocenzo G. Casella

Papers

Study of the electrochemical deposition and properties of cobalt oxide species in citrate alkaline solutions

Voltammetric and XPS investigations of nickel hydroxide electrochemically dispersed on gold surface electrodes

Electrocatalytic oxidation and liquid chromatographic detection of aliphatic alcohols at a nickel-based glassy carbon modified electrode

Electrodeposition of cobalt oxide films from carbonate solutions containing Co(II)–tartrate complexes

Copper dispersed into polyaniline films as an amperometric sensor in alkaline solutions of amino acids and polyhydric compounds